1. Field of the Invention
The present invention relates to liquid-crystal-line compounds of the formulae I and II EQU Z.sup.1 --(X.sup.1 --R.sup.1 --Y--M).sub.m I EQU Z.sup.2 --(X.sup.2 --R.sup.1 --Y--M).sub.n II
where
Z.sup.1 is the alcoholate or acid radical Z.sup.1 /1 of an m-valent aliphatic alcohol or of an m-valent aliphatic carboxylic acid having 3 to 30 carbon atoms; the alcoholate or acid radical Z.sup.1 /2 of an m-valent cycloaliphatic alcohol or of an m-valent cycloaliphatic carboxylic acid having 5 or 6 ring members, in the case where m=3, the nitrogen-containing radical Z.sup.1 /3 ##STR1## where p may be 1 or 2, in the case where m=3, a radical having the structure Z.sup.1 /4a-d ##STR2## in the case where m=3 or m=4, the acid radical Z.sup.1 /5 of nitrilotriacetic acid or of ethylenediaminetetraacetic acid, the radical Z.sup.1 /6 ##STR3## where q may be 2 or 3, Z.sup.2 is the n-valent radical Z.sup.2 /1 of a benzene ##STR4## where R.sup.2 may be halogen, cyano, nitro, C.sub.1 -C.sub.10 -alkyl, C.sub.1 - to C.sub.10 -alkoxy, C.sub.1 - to C.sub.10 -alkoxycarbonyl, C.sub.1 - to C.sub.10 -acyloxy or radicals which are bonded to the ring in the vicinal position, r is zero to 3, and the radicals R.sup.2, in the case where r&gt;1, may be identical or different, the polycyclic radical Z.sup.2 /2 ##STR5## where R.sup.3 may be C.sub.1 - to C.sub.4 -alkyl, C.sub.1 - to C.sub.4 -alkoxy or halogen, in the case where n=3, the phosphorus-containing radical Z.sup.2 /3 ##STR6## where s may be zero or 1; X.sup.1 is a chemical bond or --CO--, PA1 X.sup.2 is oxygen, sulfur, --CO--O--, --O--CO--, --SO.sub.2 --, --SO.sub.2 --O--, --O--SO.sub.2 --O--, NR.sup.4 --, --CO--NR.sup.4 --, --NR.sup.4 --O-- or --CO--N&lt;, where R.sup.4 may be hydrogen or C.sub.1 - to C.sub.8 - alkyl, with the proviso that, in the case of the polycyclic radical Z.sup.2 /2, X.sup.2 can only be --O-- or --O--CO--, PA1 m is 3 to 6, with the proviso that m is less than or equal to the number of carbon atoms in Z.sup.1, PA1 n is 3 to 6, PA1 R.sup.1 is a C.sub.2 - to C.sub.20 -bridge containing 2 to 12 bridging members, which may be interrupted by oxygen, sulfur or --NR.sup.4 --, it being possible for each of these hetero units to be separated by at least 2 carbon atoms, PA1 Y is a chemical bond, oxygen, sulfur, --CO--O--, --O--CO--, --NR.sup.4 --, --CO--NR.sup.4 -- or --NR.sup.4 --CO--, and PA1 M is a mesogenic group derived from a compound which, in the liquid-crystalline phase, has an anisotropy of the dielectric constant .epsilon. where .vertline..DELTA..epsilon..vertline.&gt;0.3 and/or which is optically active. PA1 the nematic phase, the cholesteric phase and the smectic phase. PA1 S denotes a smectic liquid-crystalline phase or smectic liquid-crystalline behavior, PA1 N denotes a nematic liquid-crystalline phase or nematic liquid-crystalline behavior, PA1 N* denotes a cholesteric (chiral nematic) liquid-crystalline phase or cholesteric (chiral nematic) liquid-crystalline behavior, where means that the liquid-crystalline compound contains a chiral, ie. optically active, center and it is PA1 glycerol, PA1 1,2,4-butanetriol, PA1 2-methyl-2-hydroxymethyl-1,3-propanediol, PA1 2-ethyl-2-hydroxymethyl-1,3-propanediol, PA1 1,2,3,4-butanetetraol, PA1 pentaerythritol, PA1 xylitol, PA1 mannitol and PA1 sorbitol, PA1 1,2,3-propanetricarboxylic acid, PA1 1,1,4-butanetricarboxylic acid, PA1 1,2,3,4-butanetetracarboxylic acid, PA1 citric acid and PA1 2-hydroxynonadecyl-1,2,3-tricarboxylic acid, PA1 1,2,3,4-tetrahydroxycyclopentane, PA1 1,2,3-trihydroxycyclohexane, PA1 1,2,4-trihydroxycyclohexane, PA1 1,3,5-trihydroxycyclohexane, PA1 1,2,3,4-tetrahydroxycyclohexane, PA1 1,2,3,5-tetrahydroxycyclohexane, PA1 1,2,4,5-tetrahydroxycyclohexane, PA1 1,2,3,4,5-pentahydroxycyclohexane and PA1 1,2,3,4,5,6-hexahydroxycyclohexane, PA1 1,2,3-cyclopentanetricarboxylic acid, PA1 1,2,4-cyclopentanetricarboxylic acid, PA1 2-methyl-1,2,3-cyclopentanetricarboxylic acid, PA1 3-methyl-1,2,4-cyclopentanetricarboxylic acid, PA1 1,1,2,2-cyclopentanetetracarboxylic acid, PA1 1,2,2,4-cyclopentanetetracarboxylic acid, PA1 1,1,3,3-cyclopentanetetracarboxylic acid, PA1 1,2,3,4-cyclopentanetetracarboxylic acid, PA1 1,2,3,4,5-cyclopentanepentacarboxylic acid, PA1 1,1,4-cyclohexanetricarboxylic acid, PA1 1,2,4-cyclohexanetricarboxylic acid, PA1 1,3,5-cyclohexanetricarboxylic acid, PA1 1,1,3,3-cyclohexanetetracarboxylic acid, PA1 1,1,4,4-cyclohexanetetracarboxylic acid, PA1 1,2,3,4-cyclohexanetetracarboxylic acid, PA1 1,2,4,5-cyclohexanetetracarboxylic acid, PA1 1,1,3,3,5-cyclohexanepentacarboxylic acid and PA1 1,2,3,4,5,6-cyclohexanehexacarboxylic acid, PA1 triethanolamine, PA1 triisopropanolamine and PA1 aminoethylethanolamine, PA1 cyanuric acid, PA1 thiocyanuric acid, PA1 melamine and PA1 trishydroxyethyl isocyanurate, PA1 1,2,3-trihydroxybenzene, PA1 1,2,4-trihydroxybenzene, PA1 1,3,5-trihydroxybenzene, PA1 1,2,3,4-tetrahydroxybenzene, PA1 1,2,3,5-tetrahydroxybenzene, PA1 1,2,4,5-tetrahydroxybenzene, PA1 hexahydroxybenzene, PA1 1,2,3-benzenetricarboxylic acid, PA1 1,2,4-benzenetricarboxylic acid, PA1 1,3,5-benzenetricarboxylic acid, PA1 3,4,5-trihydroxybenzoic acid, PA1 methyl 3,4,5-trihydroxybenzoate, PA1 1,2,3-trihydroxytoluene, PA1 2,4,5-trihydroxytoluene, PA1 2,4,6-trihydroxytoluene, PA1 3,4,5-trihydroxytoluene, PA1 pyromellitic anhydride, PA1 1,2,3,4-tetrahydroxynaphthalene, PA1 2,3,4-trihydroxyanthracene, PA1 1,2,3-trihydroxy-9,10-anthraquinone and PA1 1,2,4-trihydroxy-9,10-anthraquinone. PA1 1,3,5-trihydroxybenzene, PA1 pyromellitic anhydride and PA1 methyl 3,4,5-trihydroxybenzoate, and PA1 --(CH.sub.2).sub.2 --, --(CH.sub.2).sub.3 --, --(CH.sub.2).sub.4 --, --(CH.sub.2).sub.5 --, --(CH.sub.2).sub.6 --, --(CH.sub.2).sub.7 --, --(CH.sub.2).sub.8 --, --(CH.sub.2).sub.10 --, --(CH.sub.2).sub.12 --, --(CH.sub.2 --O--CH.sub.2).sub.2 --, ##STR13## PA1 A is 1,4-phenylene or 2,6-naphthylene, which may contain up to two nitrogen atoms as hetero atoms and may carry up to two fluorine, chlorine, bromine, nitro or cyano substituents, or is 1,4-cyclohexylene, which may contain up to two hetero atoms from oxygen, sulfur and nitrogen, in each case in non-adjacent positions, PA1 B is a chemical bond or one of the following bridging members: PA1 t is a number from 1 to 4, with the proviso that A and B may be different from one another, and PA1 u is 1 if D.sup.1 is linked to an aromatic ring and PA1 1 or 2 if D.sup.1 is linked to a cyclohexylene ring.
The invention also relates to processes for the preparation of the compounds I and II, and to the use thereof in the form of solid or liquid-crystalline, optically anisotropic media for the display and storage of information.
2. Description of the Prior Art
Liquid-crystalline compounds are optically anisotropic substances which, in contrast to liquids, have a long-range order of the molecules, it being possible for the molecules to have a regular one- or two-dimensional arrangement and to form liquid-crystalline mesophases. With respect to the spatial arrangement of the molecular units within the liquid crystal, a distinction is made between essentially 3 phases:
In nematic phases, the individual molecules are aligned in one direction. Their structural feature is a parallel alignment of the molecular long axes at the same time as a random distribution of the molecular centers of gravity. The molecules have no lateral cohesion; there is therefore no layer structure as in the smectic phases described below. The molecules can move relative to one another along their long axes, ie. they can slip past one another freely, which causes their low viscosity. Nematic phases therefore have much lower viscosity than smectic phases.
The structure of the cholesteric phase, which can only be achieved with optically active molecules, is closely related to that of the nematic phase. It is therefore frequently also known as the chiral nematic phase. As in the nematic phase, the molecular long axes of the liquid-crystalline compounds are aligned parallel to one another, but the preferential direction of the molecular long axes changes regularly from layer to layer through a certain angle. Within an individual layer, a uniform preferential direction exists which is twisted in the same direction through a constant angle with respect to the preferential direction within the adjacent layer. A helical arrangement of the molecular long axes thus forms over a plurality of layers. The helical structure is caused by the chirality of the participating molecules.
Smectic phases have a two-dimensional structure. Intermolecular interactions cause the elongate, rod-like molecules aligned parallel to one another to form layers, which are stacked at identical separations from one another. Various modifications can occur here, differing in the arrangement of the molecules within the layers. Smectic phases S.sub.A to S.sub.I are known. For example, the centers of gravity of the molecules can be arranged randomly (S.sub.A and S.sub.C phases) or regularly (S.sub.B phase) within a layer. The molecular long axes can be parallel or tilted to the perpendiculars on a layer plane. The molecules cannot leave the layer plane since virtually no interactive forces exist between the ends of the molecules. Although this allows the layers to move slightly relative to one another, the more highly ordered state (two-dimensional structure) means that the viscosity of smectic phases is greater than for nematic phases.
Furthermore, smectic liquid-crystalline phases are known which have an electrical spontaneous polarization in the absence of an external electrical field. This polarization can be reoriented by applying an external electrical field; these phases are hence known as ferroelectric smectic liquid-crystalline phases. A typical example is the chiral S.sub.c phase (S.sub.c * phase). Due to their anisotropic optical and dielectric properties, they can be utilized for electro-optical display elements (abbreviated to displays). Thus, ferroelectric displays based on S.sub.c * phases allow extremely rapid writing and deletion of symbols.
The following symbols characterize liquid-crystalline phases or liquid-crystalline behavior:
therefore possible for optically active liquid-crystalline phases to form.
When a solid liquid-crystalline compound melts, a smectic phase, for example, is formed first as a liquid-crystalline phase; as the temperature is increased further, this is converted either into a further liquid-crystalline phase, for example a nematic phase, or, at the clearing point, into the optically isotropic melt, at phase-transition temperatures which are characteristic of each compound. When the melt is cooled, the liquid-crystalline phases and finally the crystalline liquid crystal re-format the corresponding transition temperatures. This interconversion of the liquid-crystalline compound is known as enantiotropic conversion.
Some liquid crystals are compounds in which it is possible to freeze the liquid-crystalline phase once formed. To this end, the liquid-crystalline melt is cooled below a certain temperature, so that an optically anisotropic solid is formed which is not crystalline, but glassy.
Liquid-crystalline compounds which solidify to form glass-like materials are found both amongst low-molecular-weight organic compounds and amongst polymeric organic compounds. In known polymeric liquid crystals, polyacrylic and polymethacrylic chains, inter alia, serve as the main polymer chains. Structural units of low-molecular-weight liquid-crystalline compounds as side groups are linked to this polymer backbone via polymeranalogous reactions.
EP-B 90 282 discloses polymers based on esters and amides of acrylic acid and methacrylic acid which form liquid-crystalline phases. The side chains linked to the main polymer chain via the ester and amide functions comprise a flexible, long-chain moiety which maintains the separation (also known as a spacer) and a mesogenic group or pleochroic dye and effect the formation of liquid-crystalline phases.
Suitable spacers are alkylene groups having 2 to 12 carbon atoms which may be linear or branched and may be interrupted by oxygen, sulfur and/or R.sup.6 --N&lt; groups where R.sup.6 is hydrogen or substituted or unsubstituted alkyl.
Examples of mesogenic groups are those mentioned, for example, in Kelker and Hatz, Handbook of Liquid Crystals, Verlag Chemie 1980, pages 69 to 113.
Depending on the spacers and/or mesogenic groups, the polymers may form liquid-crystalline phases and can be employed alone or together with low-molecular-weight liquid crystals in electro-optical displays.
In principle, the electro-optical displays comprise a 6 to 30 .mu.m liquid-crystalline layer between two glass plates, each of which is coated on the inside with an electrode layer and at least one of which must be transparent. The transparent, electroconductive top layers used are in particular antimony-doped tin oxide layers and tin oxide-doped indium oxide layers.
DE-A 39 17 196 discloses monomers of the formula V ##STR7## where R.sup.7 is hydrogen, chlorine or methyl, E is a flexible spacer, F is a mesogenic moiety which is built up from at least three aromatic rings linked in a linear or approximately linear manner and which contains at least one 2,6-naphthalene group, and G is an optically active chiral moiety. These monomers are used to prepare polymers containing chiral mesogenic side groups with a ferroelectric smectic liquid-crystalline behavior.
A disadvantage of using polymeric liquid crystals is the slow speed of the switching processes. A further disadvantage is that polymeric liquid crystals, unlike low-molecular-weight compounds, cannot be synthesized in a uniform, defined molecular weight.
Known low-molecular-weight liquid crystals include liquid-crystalline compounds having glass phases, which can be used in industry and electro-optics due to their characteristic phase properties.
DE-A 37 03 640 describes glass-like, liquid-crystalline, 2-substituted 1,4-bis(4-substituted benzoyloxy)benzenes. They are employed alone, in mixtures with one another or with other liquid-crystalline or non-liquid-crystalline substances as anisotropic, solid, optical media for the production of optical components and for thermoelectro-optical storage displays at room temperature.
Corresponding areas of application exist for the 1,4-bis(2,3,4-substituted benzoyloxy)benzenes disclosed in DE-A 38 30 968, which form nematic phases which solidify to form glass-like materials.
DE-A 38 27 603 discloses chiral, smectic liquid-crystalline compounds of the formula VI EQU M.sub.1 *--K--M.sub.2* VI
where M.sub.1 * and M.sub.2 * are identical chiral, smectogenic groups, and --K-- is a divalent group. They have the property of simultaneously solidifying from the liquid-crystalline phase on cooling to give glass-like materials.
The low-molecular-weight liquid-crystalline compounds having glass phases known hitherto have the common property that their glass phases do not have long-term stability and therefore take on a crystalline ordered state after a brief time at room temperature. The information previously written is lost due to this crystallization process. A further disadvantage is their low anisotropy of the dielectric constant .DELTA..epsilon., which is crucial for the alignment of the molecules in the electrical field. The dielectric anisotropy is the difference between the dielectric constants .epsilon. measured parallel and perpendicular to the resultant preferential direction given from the alignment of all the molecular long axes. The values for the dielectric constant .epsilon. measured parallel to the preferential direction are denoted by .epsilon..parallel. and the values measured perpendicular thereto are denoted by .epsilon..sub..perp.. The dielectric anisotropy (.DELTA..epsilon.=.epsilon..parallel.-.epsilon..sub..perp.) may be positive or negative. If .epsilon..parallel. is greater than .epsilon..sub..perp. and .DELTA..epsilon. is thus positive, the liquid crystal aligns itself with its optical axis parallel to the field. If .DELTA..epsilon. is negative, the optical axis aligns itself perpendicular to the field.